Distributed and Cable reduced TCAS

ABSTRACT

A direction finding antenna system for determining the relative bearing of a second aircraft from a first aircraft in conjunction with a Traffic Alert Collision Avoidance System (TCAS). The system includes a first antenna and a second antenna located on a top surface of the first aircraft, spaced apart along a first axis, as well as a third antenna and a fourth antenna located on a bottom surface of the first aircraft, spaced apart along a second axis orthogonal to the first axis. The system further includes a transmitting, receiving, and processing system coupled to the first, second, third, and fourth antennas, wherein the transmitting, receiving, and processing system is configured to transmit TCAS interrogations, receive TCAS replies, and process the TCAS replies to determine the relative bearing of the second aircraft from the first aircraft.

PRIORITY CLAIM

This invention claims priority from U.S. Provisional Application No.60/826,030, entitled “DISTRIBUTED AND CABLE REDUCED TCAS,” filed Sep.18, 2006 which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Current Traffic Alert Collision Avoidance (TCAS) installations areexpensive. Dual TCAS installations are even more so because they requirean extensive amount of cable and/or coaxial cable switches. StandardTCAS antennas also do not typically have a wide enough bandwidth toprovide for integration of all L-band avionics equipment such as TCAS,Distance Measuring Equipment (DME) and transponder (XPDR) using the sameantennas. U.S. Pat. No. 4,855,748, incorporated herein by referencedescribes a system and method for determining TCAS bearing estimationusing a four element planar array antenna. TCAS installations typicallyuse two such four element antennas, one on the top surface of anaircraft, and the other on the bottom surface of the aircraft. Thistypically requires a coaxial cable connection for each antenna element,resulting in at least eight total cables and an extensive number ofcoaxial cable switches. This results in considerable complexity andexpense. U.S. Pat. No. 6,222,480, incorporated herein by reference,describes a system and method that integrates TCAS and XPDR functions.However, the system and method described in the '480 patent use a topfour element antenna and a bottom four element antenna that results inextensive cable and coaxial switch requirements. Accordingly, there is aneed for a TCAS antenna system that uses less cable and coaxial switchesand is thus less expensive.

The '748 and '480 patents also use a single transmitting, receiving, andprocessing unit. This has the disadvantage of not offering anyredundancy should the transmitting, receiving, and processing unitbecome damaged or malfunction. Accordingly, there is a further need fora TCAS system offering some level of redundancy.

SUMMARY OF THE INVENTION

The present invention includes a direction finding antenna system fordetermining the relative bearing of a second aircraft from a firstaircraft in conjunction with a Traffic Alert Collision Avoidance System(TCAS), the second aircraft being equipped to transmit signals receivedby the antenna system. The system includes a first antenna and a secondantenna located on a top surface of the first aircraft, spaced apartalong a first axis, as well as a third antenna and a fourth antennalocated on a bottom surface of the first aircraft, spaced apart along asecond axis orthogonal to the first axis. The system also includes atransmitting, receiving, and processing system coupled to the first,second, third, and fourth antennas, wherein the transmitting, receiving,and processing system is configured to transmit TCAS interrogations,receive TCAS replies, and process the TCAS replies to determine therelative bearing of the second aircraft from the first aircraft.

In accordance with further aspects of the invention, the transmitting,receiving, and processing system is further configured to transmittransponder signals. In accordance with other aspects of the invention,the first, second, third, and fourth antennas are L-band blade antennasin an example embodiment. In accordance with still further aspects ofthe invention, the transmitting, receiving, and processing systemincludes a transmitter selectively coupled to at least one of the first,second, third, and fourth antennas, the transmitter configured totransmit TCAS interrogations omnidirectionally.

In accordance with yet other aspects of the invention, the transmitting,receiving, and processing system includes a line replaceable unit (LRU),the LRU including a receiver selectively coupled to the first, second,third, and fourth antennas. In accordance with still another aspect ofthe invention, the receiver includes a first phase detector fordetecting the phase of signals received from the first antenna, a secondphase detector for detecting the phase of signals received from thesecond antenna, a third phase detector for detecting the phase ofsignals received from the third antenna, and a fourth phase detector fordetecting the phase of signals received from the fourth antenna.

In accordance with still further aspects of the invention, thetransmitting, receiving, and processing system includes a first linereplaceable unit (LRU) and a second LRU in signal communication with thefirst LRU. In accordance with yet other aspects of the invention, thefirst LRU includes a first receiver selectively coupled to the firstantenna and the third antenna and the second LRU includes a secondreceiver selectively coupled to the second antenna and the fourthantenna. In accordance with still further aspects of the invention, thefirst receiver includes a first phase detector for detecting the phaseof signals received from the first antenna and a second phase detectorfor detecting the phase of signals received from the third antenna. Inan additional aspect of the invention, the first and second phasedetectors also include a first amplitude detector and a second amplitudedetector respectively for sensing the amplitude of signals received fromthe first antenna and the third antenna.

As will be readily appreciated from the foregoing summary, the inventionprovides a TCAS antenna system that uses less cabling than previousattempts. The invention further provides a TCAS antenna system withintegrated TCAS and XPDR that uses less cabling than previous attempts.The invention still further provides a TCAS antenna system havingdistributed receiving and processing units and less cabling thanprevious attempts. This provides some redundancy so that if one of thetransmitting, receiving, and processing units ceases to functionproperly, some functionality remains. In an example embodiment, atransmitter is present in each unit, and all transmission functionalityremains if either unit ceases to function properly. However, in theexample embodiment, some receiver functions are distributed between thetwo units such that if either unit ceases to function properly thefunction will be lost. For example, azimuth estimation of a receivedsignal is a distributed function and will be lost if either unit ceasesto function properly.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 is a high-level block diagram showing an antenna configurationfor a TCAS system in accordance with an embodiment of the invention;

FIG. 2 is a high-level block diagram showing an antenna configurationfor a TCAS system formed in accordance with an alternate embodiment ofthe invention;

FIG. 3 is a block diagram showing additional detail for the embodimentshown in FIG. 1;

FIG. 4 is a block diagram showing additional detail for the alternateembodiment shown in FIG. 2;

FIG. 5 is a block diagram showing additional detail for the embodimentshown in FIGS. 1 and 3; and

FIG. 6 is a block diagram showing additional detail for the embodimentshown in FIGS. 2 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In an embodiment, the invention uses 4 cables to implement a TrafficAlert Collision Avoidance System (TCAS) and uses standard L-band bladeantennas. This simplifies L-band integration because the standard L-bandblade handles TCAS, transponder (XPDR), and Distance Measuring Equipment(DME) frequencies. In an alternative embodiment, the TCAS receivefunction is distributed between two units that each have one receiverswitched between two antenna ports. This further reduces the cost of theTCAS receive function. Although each unit is stated to include onereceiver, it should be understood that each receiver includes aplurality of receiving components in some embodiments, with eachcomponent including a reception channel that is referred to as areceiver in some embodiments.

In an embodiment, TCAS surveillance is performed using anomnidirectional transmit pattern, thereby allowing the use of a standardL-Band transponder and/or DME antenna. TCAS bearing measurements aremade by utilizing two L-band blade antennas on a top portion of anaircraft and two L-band blade antennas on a bottom portion of theaircraft. However, in other embodiments, a two element top antenna and atwo element bottom antenna are used. This example implementation uses 4TCAS cables. The two sets of L-band blades are orthogonally oriented. Inan alternative embodiment, the TCAS receive function is distributedbetween two units where each unit is connected to one top and one bottomL-band blade. The two antenna blades on the top are mounted orthogonallyto the two antenna blades on the bottom. In an additional embodiment,transponder functions are also integrated in the TCAS system by usingthe same antennas and DME functionality may use the same antennas aswell.

FIG. 1 is a high-level block diagram showing a TCAS system 40 formed inaccordance with an embodiment of the invention. The system 40 includes afirst top antenna 42, a second top antenna 44, a first bottom antenna46, and a second bottom antenna 48. Each of the antennas 42, 44, 46, and48 are connected to a transmitting, receiving, and processing system 49by a cable 52, resulting in four total cables 52 for the system 40. Thesystem 49 includes a Line Replaceable Unit (LRU) 50, designated as TPL4that includes transmitting, receiving, and processing components.

When installed on an aircraft, the first top antenna 42 and the secondtop antenna 44 are positioned on a top surface of the aircraft, spacedapart along a first axis while the first bottom antenna 46 and thesecond bottom antenna 48 are positioned on a bottom surface of theaircraft, spaced apart along a second axis orthogonal to the first axis.In an example embodiment, the antennas 42, 44, 46, 48 are L-band bladeantennas. In one example, an L-band blade antenna is any single elementL-band antenna suitable for transponder or DME applications, and may bea simple, standard matched-quarter-wave stub antenna. In comparison toprior art systems using two four element array antennas, the system 40shown in FIG. 1 gives a 50% port reduction, simplifies DME integrationif using omnidirectional transmission, simplifies radio frequency (RF)systems required, transmits omnidirectionally, offers a simplifiedantenna configuration with fewer cables, and offers a potential sizereduction. However, in other embodiments, the system 40 transmits TCASinterrogation signals by forming a beam using at least two of theantennas 42, 44, 46, and 48 rather than transmitting omnidirectionally.

FIG. 2 is a high-level block diagram showing a TCAS system 60 formed inaccordance with an alternate embodiment of the invention. In similarfashion to the system 40, the system 60 includes a first top antenna 62,a second top antenna 64, a first bottom antenna 66, and a second bottomantenna 68 connected to a transmitting, receiving, and processing system69 using four cables 52. As for the system 40, the first top antenna 62and the second top antenna 64 are positioned on a top surface of anaircraft, spaced apart along a first axis while the first bottom antenna66 and the second bottom antenna 68 are positioned on a bottom surfaceof the aircraft, spaced apart along a second axis orthogonal to thefirst axis. However, the system 69 is different from the system 49 inthat the system 69 includes a first LRU 70 and a second LRU 72, each ofthe units 70, 72 designated as TPL2 and being connected to only twoantennas. The first unit 70 is in signal communication with the secondunit 72 over a communications link 74. Although the link 74 is shown asa single connection, multiple connection channels are present in anexample embodiment.

The first unit 70 is connected to the antennas 62, 66 and the secondunit 72 is connected to the antennas 64, 68. In an example embodiment,the antennas 62, 64, 66, 68 are L-band blade antennas. In one example,an L-band blade antenna is any single element L-band antenna suitablefor transponder or DME applications, and may be a simple, standardmatched-quarter-wave stub antenna. In comparison to prior art systemsusing two planar four element array antennas, the system 60 gives a 75%port reduction, simplifies DME integration, simplifies RF systems,transmits omnidirectionally, offers a simplified antenna configurationwith fewer cables, offers a size reduction, and has a bearing suppliedby dual units 70, 72. The system 60 also offers limited dual TCAScapability because the use of both the first unit 70 and the second unit72 is only required for bearing determination, but not for range andaltitude determination. Accordingly, if one of the units 70, 72 is lostdue to damage, malfunctioning, or other reasons, bearing determinationis lost but other functions are still operable.

FIG. 3 is a block diagram showing additional detail for the LRU 50 shownin FIG. 2. In an example embodiment, the LRU 50 includes a switch 80connected to a transmitter 82 and a receiver 84. In an exampleembodiment, the receiver 84 uses the methods described in U.S. Pat. No.4,855,748 to determine bearing information. Although the connectionsbetween the switch 80 and the transmitter 82 and receiver 84 are shownas single links, multiple connections exist in an example embodiment. Anintermediate frequency (IF)/synthesizer module 86 is in signalcommunication with both the transmitter 82 and the receiver 84. Aprocessor 88 is in signal communication with the receiver 84. The switch80 is used to selectively connect the antennas 42, 44, 46, and 48 to thetransmitter 82 and the receiver 84.

FIG. 4 is a block diagram showing additional detail for the LRUs 70, 72shown in FIG. 2. In an example embodiment, the LRU 70 includes a switch90 connected to a receiver 92 that is in signal communication with aprocessor 94. The LRU 70 also includes an IF/synthesizer module 96 insignal communication with the receiver 92 and a transmitter 98. Thetransmitter 98 is also connected to the switch 90. The switch 90 is usedto selectively connect the antennas 62, 66 to the receiver 92 and thetransmitter 98. Similarly, the LRU 72 includes a switch 100 connected toa receiver 102 that is in signal communication with a processor 104. TheLRU 72 also includes an IF/synthesizer module 106 in signalcommunication with the receiver 106 and a transmitter 108. Thetransmitter 108 is also connected to the switch 100. The switch 100 isused to selectively connect the antennas 64, 68 to the receiver 102 andthe transmitter 108. The processor 94 is in signal communication withthe processor 104 using the link 74. In an example embodiment, thereceivers 92, 106 use the methods described in U.S. Pat. No. 4,855,748to determine bearing information and one of the LRUs 70, 72 transmitsinterrogations, determines range, and decodes replies.

FIG. 5 is a block diagram showing additional detail for the LRU 50 shownin FIGS. 1 and 3. In an example embodiment, the switch 80 includes a topTX/RX switch 120, a bottom TX/RX switch 122, and a Top/Bottom switch124. The Top/Bottom switch 124 is used to selectively connect thetransmitter 82 to the top TX/RX switch 120 or the bottom TX/RX switch122. The TX/RX switches 120, 122 are used to selectively connect theantenna 44 and the antenna 48, respectively to the receiver 84 or thetransmitter 82. In an example embodiment, the switches 120, 122, 124 arecontrolled by the processor 88 (connections not shown).

The receiver 84 includes a first RX filter 126 whose input is connectedto the first top antenna 42, a second RX filter 128 whose input isconnected to the top TX/RX switch 120 so that it may be selectivelyconnected to the second top antenna 44, a third RX filter 130 whoseinput is connected to the first bottom antenna 46, and a fourth RXfilter 132 whose input is connected to the bottom TX/RX switch 122 sothat it may be selectively connected to the second bottom antenna 48.Each of the RX filters 126, 128, 130, and 132 has its output connectedto the input of a Low Noise Amplifier (LNA) 134, 136, 138, 140respectively. The outputs of the LNAs 134, 136, 138, 140 are connectedto one of two inputs of a down converter 142, 144, 146, 148respectively. The other input to the down converters 142, 144, 146, 148is received from an output of the IF/synthesizer module 86.

Each output from the down converters 142, 144, 146, 148 then passes intoa detection and bearing processing component 150. The detection andbearing processing component 150 includes first, second, third, andfourth phase detectors 152, 154, 156, and 158 respectively. Each phasedetector 152, 154, 156, 158 takes as its input, the output of the downconverters 142, 144, 146, 148 respectively. The outputs of the phasedetectors 152, 154, 156, 158 are then used as inputs to a bearingprocessor 160. The detection and bearing processing component 150 isalso in signal communication with the processor 88 so that the output ofthe bearing processor 160 may be used by the processor 88 for furtherprocessing and display, and so the processor 88 is able to providecontrol signals to the receiver 84. Although not shown for clarity,alternative embodiments include first, second, third, and fourth signalamplitude detectors that are used in conjunction with the phasedetectors 152, 154, 156, and 158 in an example embodiment to provideadditional information used by the bearing processor 160 in determiningbearing.

The IF/Synthesizer module 86 includes a radiofrequency (RF) source 162in signal communication with a modulator 164. An output of the RF source162 is used as an input to the down converters 142, 144, 146, and 148.An output of the modulator 164 is used as an input to the transmitter82. The transmitter 82 includes a programmable attenuator 166 whoseinput is received from the modulator 164 output. The output of theprogrammable attenuator 166 next passes to the input of a poweramplifier (PA) 168. The output of the PA 168 is in signal communicationwith the input of a TX filter 170, whose output is connected to theTop/Bottom switch 124.

FIG. 6 is a block diagram showing additional detail for the LRU 70 shownin FIGS. 2 and 4. In an example embodiment, the switch 90 includes a topTX/RX switch 190, a bottom TX/RX switch 192, and a Top/Bottom switch194. The Top/Bottom switch 194 is used to selectively connect thetransmitter 98 to the top TX/RX switch 190 or the bottom TX/RX switch192. The TX/RX switches 190, 192 are used to selectively connect thefirst top antenna 62 and the first bottom antenna 66, respectively tothe receiver 92 or the transmitter 98. In an example embodiment, theswitches 190, 192, 194 are controlled by the processor 94 (connectionsnot shown).

The receiver 92 includes a first phase detector 196 and a second phasedetector 198. A first input of the first phase detector 196 isselectively connected to the first top antenna 62 by the top TX/RXswitch 190. In similar fashion, a first input of the second phasedetector 198 is selectively connected to the first bottom antenna 66 bythe bottom TX/RX switch 192. In an example embodiment, filtering,amplification, and down conversion stages (not shown) are presentbetween the switches 190, 192 and the phase detectors 196, 198 insimilar fashion to those shown in FIG. 5 for the system 40. Each of thephase detectors 196, 198 also receives a second input from the secondunit 72, such as a phase reference signal from the processor 104 overthe communications link 74, for example.

The outputs of the phase detectors 196, 198 are then used as inputs to abearing processor 200. The bearing processor 200 also receives as inputsthe top and bottom phases from the second top antenna 64 and the secondbottom antenna 68, received from the second unit 72 over the link 74,for example. The bearing processor 200 is also in signal communicationwith the processor 94 so that the output of the bearing processor 200may be used by the processor 94 for further processing and display, andso the processor 94 is able to provide control signals to the receiver92. The processor 94 is also in signal communication with the processor104 of the second unit 72 over the link 74. The second unit 72, althoughnot shown in FIG. 6, is configured similarly to the first unit 70.

An output of the IF/Synthesizer module 96 is used as an input to thetransmitter 98. In an example embodiment, the IF/Synthesizer module 96includes a radiofrequency (RF) source in signal communication with amodulator (both not shown) with an output of the RF source being used asan input to down converters (not shown) used in the receiver 92 insimilar fashion to those shown in FIG. 5 for the system 40. An output ofthe transmitter 82 is connected to the Top/Bottom switch 194. In anexample embodiment, the transmitter 82 includes a programmableattenuator and a power amplifier (both not shown) in similar fashion tothose shown in FIG. 5 for the system 40.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. For example, rather thanusing L-band blade antennas, L-band antennas integrated into skinsurfaces of an aircraft could be used in some embodiments. Additionally,a top two-element antenna and a bottom two-element antenna are used insome embodiments, with the first antenna being replaced by the firstelement of the top two-element antenna, the second antenna beingreplaced by the second element of the top two-element antenna, the thirdantenna being replaced by the first element of the bottom two-elementantenna, and the fourth antenna being replaced by the second element ofthe bottom two-element antenna. Accordingly, the scope of the inventionis not limited by the disclosure of the preferred embodiment. Instead,the invention should be determined entirely by reference to the claimsthat follow.

1. A direction finding antenna system located on a first aircraft for determining the relative bearing of a second aircraft from the first aircraft in conjunction with a Traffic Alert Collision Avoidance System (TCAS), the second aircraft being equipped to transmit signals received by the antenna system, the system comprising: a first antenna and a second antenna located on a top surface of the first aircraft, spaced apart along a first axis; a third antenna and a fourth antenna located on a bottom surface of the first aircraft, spaced apart along a second axis orthogonal to the first axis; and a transmitting, receiving, and processing system coupled to the first, second, third, and fourth antennas, wherein the transmitting, receiving, and processing system is configured to transmit TCAS interrogations, receive TCAS replies, and process the TCAS replies to determine the relative bearing of the second aircraft from the first aircraft, wherein the transmitting, receiving, and processing system includes a transmitter selectively coupled to at least one of the first, second, third, and fourth antennas, the transmitter configured to transmit TCAS interrogations omnidirectionally, and wherein each of the first antenna, the second antenna, the third antenna, and the fourth antenna have only a single element.
 2. The system of claim 1, wherein the transmitting, receiving, and processing system is further configured to transmit transponder signals.
 3. The system of claim 1, wherein the first, second, third, and fourth antennas are L-band blade antennas.
 4. The system of claim 1, wherein the transmitter is further configured to transmit TCAS interrogations by generating a directional beam using at least two of the first, second, third, and fourth antennas.
 5. The system of claim 1, wherein the transmitting, receiving, and processing system includes a line replaceable unit (LRU), the LRU including a receiver selectively coupled to the first, second, third, and fourth antennas.
 6. The system of claim 5, wherein the receiver includes a first detector for detecting an aspect of signals received from the first antenna, a second detector for detecting an aspect of signals received from the second antenna, a third detector for detecting an aspect of signals received from the third antenna, and a fourth detector for detecting an aspect of signals received from the fourth antenna.
 7. The system of claim 6, wherein the first, second, third, and fourth detectors each include a phase detector for detecting the phase of signals received from the first, second, third, and fourth antennas respectively.
 8. The system of claim 7, wherein the first, second, third, and fourth detectors each include an amplitude detector for detecting the amplitude of signals received from the first, second, third, and fourth antennas respectively.
 9. The system of claim 1, wherein the transmitting, receiving, and processing system comprises: a first line replaceable unit (LRU); and a second LRU in signal communication with the first LRU wherein the first and second LRUs are configured to process bearing information in a distributed manner.
 10. The system of claim 9, wherein the first LRU includes a first receiver selectively coupled to the first antenna and the third antenna and the second LRU includes a second receiver selectively coupled to the second antenna and the fourth antenna.
 11. The system of claim 10, wherein the first receiver includes a first phase detector for detecting the phase of signals received from the first antenna and a second phase detector for detecting the phase of signals received from the third antenna.
 12. A direction finding antenna system located on a first aircraft for determining the relative bearing of a second aircraft from the first aircraft in conjunction with a Traffic Alert Collision Avoidance System (TCAS), the second aircraft being equipped to transmit signals received by the antenna system, the system comprising: a first two-element antenna located on a top surface of the first aircraft, having only a first element and a second element spaced apart along a first axis; a second two-element antenna located on a bottom surface of the first aircraft, having only a first element and a second element spaced apart along a second axis orthogonal to the first axis; and a transmitting, receiving, and processing system coupled to the first and second antennas, wherein the transmitting, receiving, and processing system is configured to transmit TCAS interrogations, receive TCAS replies, and process the TCAS replies to determine the relative bearing of the second aircraft from the first aircraft and wherein the transmitting, receiving, and processing system includes a transmitter selectively coupled to at least one of the first, second, third, and fourth antennas, the transmitter configured to transmit TCAS interrogations omnidirectionally.
 13. The system of claim 12, wherein the transmitting, receiving, and processing system is further configured to transmit transponder signals. 